The preset invention relates to a method and apparatus for generating a high contrast image of a living subject using high energy X-rays.
X-rays have been used for some time to generate images of living subjects. In previous X-ray imaging technology, X-rays are transmitted toward the living subject from an X-ray source, and are transmitted through the tissue to be imaged. The degree of transmission of the X-rays in different parts of the irradiated area of tissue varies depending on the nature of the matter or tissue through which it must pass. By measuring or determining the degree of transmission of the X-rays through the target area, an image of the irradiated area can be created.
If high-energy X-rays are used in standard X-ray imaging technology, the resulting image will have relatively little inherent contrast, especially if the area of tissue imaged consists only of soft tissue, as compared to a combination of soft tissue and bone.
The problem of generating high contrast images of soft tissue is especially important in oncologic imaging. The ability to distinguish tumors from surrounding soft tissue is extremely useful in diagnosis and treatment of cancer.
Furthermore, it is necessary to image these structures both in their three-dimensional relationship (3-D or cross-sectional images) and from the "beam's eye" point of view, as projected 2-D images, in order to support the treatment of tumors by radiation therapy. In this therapeutic modality, high-energy X-ray beams are placed so as to deliver the greatest possible dose to the tumor and to spare as much as possible normal tissues. Currently, films or electronic images are used to plan and verify the proper placement, shape and dimension of the treatment beam, while cross-sectional and volumetric images are obtained by computed tomography (CT) or magnetic resonance imaging (MRI). The information obtained from these various modalities is then manipulated by computer and used to design a patient-specific treatment plan. These activities are lengthy, expensive, and potentially fraught with uncertainties deriving from the lack of a direct, fast method for visualizing the treatment volume within the patient in the actual device and in the position used for treatment, as well as the need for extensive computer modeling and simulation.
Finally, even more than in diagnostic imaging modalities, a method capable of giving real-time images would be of particular usefulness when used in support of radiosurgery. Such a method does not exist today. Radiosurgery is so critically dependent upon correct beam positioning that a special fixture must be constructed to guide the therapy beams delivering the treatment, which is typically limited to a single session. This has the disadvantage that fractionated treatments (treatments delivered over several sessions) are impossible or, at best, are difficult and potentially less precise. (Fractionated treatments are the mode of choice in standard therapy, offering significant biological advantages.) A method for on-the-spot, real time visualization, requiring only a modest X-ray dose, would offer the advantage of making fractionated radiosurgery practical, and both fractionated and single-dose therapy more precise and accurate.
Therefore there is a need for improved imaging apparatus and methods which have fewer problems than the prior technology.